Introduction: The effect of caffeine on acupuncture analgesia in humans is unclear. This study aimed to investigate whether caffeine-containing beverage intake influences the effect of electroacupuncture on static quantitative sensory testing (QST) and dynamic QST in healthy subjects.
Methods: A total of 40 healthy subjects were enrolled and randomly assigned to receive coffee containing moderate doses of caffeine (coffee group) or non-caffeinated juice (juice group) for 4 weeks. The primary outcome measures were the pressure pain threshold, pressure pain tolerance, and heat pain threshold as static QST parameters. Numerical rating scales (NRS) of heat stimulus and nociceptive flexor reflex (RIII reflex), as parameters of dynamic QST, were also examined.
Electroacupuncture stimulation with tolerance intensity was performed at ST36 (Zusanli)-GB34 (Yanglingquan) points at weeks 0, 2, and 4. Pressure pain threshold, pressure pain tolerance, and heat pain threshold were detected pre- and post- electroacupuncture. The NRS scores were examined pre-, during, and post-electroacupuncture, and 1 min after electroacupuncture was completed. The RIII reflex was examined pre- and 1-5 min post-electroacupuncture.
Results: At week 0, both groups showed increased pressure pain threshold and pressure pain tolerance and decreased NRS scores of heat stimuli and RIII reflex after electroacupuncture, but heat pain threshold was not affected. After 4 weeks, the effects of electroacupuncture on pressure pain threshold and pressure pain tolerance were attenuated in the coffee group compared to the juice group, whereas the effect of electroacupuncture on the NRS scores and RIII reflex were not influenced. There was no significant difference found at week 2 for these indications. Electroacupuncture also did not affect the heat pain threshold in both groups at week 4.
Conclusion: Moderate caffeine intake reduced the effects of electroacupuncture on pressure pain threshold and pressure pain tolerance in healthy subjects.